This is a community-maintained plugin! It does not ship with Logstash by default, but it is easy to install by running bin/logstash-plugin install logstash-output-solr_http.

This output lets you index&store your logs in Solr. If you want to get
started quickly you should use version 4.4 or above in schemaless mode,
which will try and guess your fields automatically. To turn that on,
you can use the example included in the Solr archive: